Survival of the fittest is, at its heart, an expression of the idea that natural selection will favor those species that are best adapted to their environment. But there might also be a place for the unfit after all.

Natural selection and survival of the fittest are often seen as synonymous, even if the truth is a bit more complicated. Still, whatever its origins, the term is a useful encapsulation of one of the driving forces of evolution...except when it isn't, as researchers at the UK's Universities of Exeter and Bath recently discovered. In certain situations, the unfit don't just survive, they thrive.

The most famous philosopher of the Victorian age, Herbert Spencer, coined the term "survival…
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It all goes back to bacteria. In the past, researchers have examined many generations of bacterial evolution and had expected to see the fittest species eventually edge out its competitors and dominate. But, as University Exeter professor Robert Beardmore explains, that wasn't quite what happened:

"Microbiologists have tested this principle by constructing very simple environments in the lab to see what happens after hundreds of generations of bacterial evolution, about 3,000 years in human terms. It had been believed that the genome of only the fittest bacteria would be left, but that wasn't their finding. The experiments generated lots of unexpected genetic diversity."

This laboratory diversity was a surprising result, and many scientists criticized the findings on the grounds that not enough time had been given for evolution to run its full course. But this new research has not just demonstrated the earlier results were no fluke, it's also shown the mechanism behind this surprising diversity. University of Bath professor Laurence Hurst explains:

"Key to the new understanding is the realisation that the amount of energy organisms squeeze out of their food depends on how much food they have. Give them abundant food and they use it inefficiently. When we combine this with the notion that organisms with different food-utilising strategies are also affected in different ways by genetic mutations, then we discover a new principle, one in which both the fit and the unfit coexist indefinitely."

The University of Exeter's Dr. Ivana Gudelj expands on this point:

"The fit use food well but they aren't resilient to mutations, whereas the less efficient, unfit consumers are maintained by their resilience to mutation. If there's a low mutation rate, survival of the fittest rules, but if not, lots of diversity can be maintained. Rather nicely, the numbers needed for the principle to work accord with those enigmatic experiments on bacteria. Their mutation rate seems to be high enough for both fit and unfit to be maintained."

So, let this be a lesson to all species - if you're starting to feel unfit, up the mutation rate. Nothing like a sudden spike in mutations to hide your basic unworthiness from the forces of natural selection.